in chapter 8.4, it is going to avoid people input a wrong product id to hack the app,
it does avoid people to do hack like this “http://localhost:3000/store/add_to_cart/widdle”
how ever, if people do things like this “http://localhost:3000/store/add_to_cart/2widdle”
the application will take the “2” as id
so, 8.4 not really solve the problem….